Topological interface states -- a possible path towards a Landau-level laser in the THz regime

TL;DR

This paper explores the potential of topological interface states, specifically Volkov-Pankratov bands, as a basis for developing a Landau-level laser operating in the THz frequency range, by controlling their Landau quantization and optical transitions.

Contribution

It demonstrates how magnetic fields and interface width can control Landau levels in topological interface states, proposing a new pathway for THz Landau-level lasers.

Findings

Landau levels can be controlled via magnetic field and interface width.

Optical coupling of Landau levels enables population inversion.

Potential for THz laser development using topological interface states.

Abstract

Volkov-Pankratov surface bands arise in smooth topological interfaces, i.e. interfaces between a topological and a trivial insulator, in addition to the chiral surface state imposed by the bulk-surface correspondence of topological materials. These two-dimensional bands become Landau-quantized if a magnetic field is applied perpendicular to the interface. I show that the energy scales, which are typically in the 10-100 meV range, can be controlled both by the perpendicular magnetic field and the interface width. The latter can still be varied with the help of a magnetic-field component in the interface. The Landau levels of the different Volkov-Pankratov bands are optically coupled, and their arrangement may allow one to obtain population inversion by resonant optical pumping. This could serve as the elementary brick of a multi-level laser based on Landau levels. Moreover, the photons are absorbed and emitted either parallel or perpendicular to the magnetic field, respectively in the Voigt and Faraday geometry, depending on the Volkov-Pankratov bands and Landau levels involved in the optical transitions.